A method of appending a digital signature based on a public key encryption system to an electronic file is widely used in order to prevent data from being altered by a third person when transmitting the electronic file to a receiver through a network is widely used. A user transmits an electronic certificate containing unique information, such as a public key and the user's name, to the receiver, with electronic data that is encoded with a private key and appended with the digital signature. The receiver can acquire the original electronic data by decoding the encoded electronic data using the public key contained in the electronic certificate. The identification of the transmitter of the electronic file and the authenticity (originality) of the electronic file can be ensured using the digital signature and the electronic certificate.
Further, in general, PDFs are provided with a digital signature function. The user can designate a desired area in the document and embed a signature form signature and a signature filed. The signature form makes it possible to verify the signature or display a window that displays the contents of an electronic certificate used for the signature, for example, by clicking a mouse. The signature field makes it possible to attach a display image and a handwritten signature, a company logo, and a photo, in order to shows the signee's information in more detail.
An image forming apparatus can append a digital signature to an electronic file generated using scan-to-PDF. However, the PDFs cannot have information on the signee appended in the signature field.